Phenolic compounds and expression of 4CL genes in silver birch clones and Pt4CL1a lines.

Suvi Sutela,Pekka Saranpää,Riitta Julkunen-Tiitto,Tapio Laakso,Tiina Ylioja,Vincent Chiang,Heidi Tiimonen,Hely Häggman,Tuija Aronen,Terhi Hahl

doi:10.1371/journal.pone.0114434

Suvi Sutela, Pekka Saranpää + Show 8 more

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https://doi.org/10.1371/journal.pone.0114434

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Abstract

A small multigene family encodes 4-coumarate:CoA ligases (4CLs) catalyzing the CoA ligation of hydroxycinnamic acids, a branch point step directing metabolites to a flavonoid or monolignol pathway. In the present study, we examined the effect of antisense Populus tremuloides 4CL (Pt4CL1) to the lignin and soluble phenolic compound composition of silver birch (Betula pendula) Pt4CL1a lines in comparison with non-transgenic silver birch clones. The endogenous expression of silver birch 4CL genes was recorded in the stems and leaves and also in leaves that were mechanically injured. In one of the transgenic Pt4CL1a lines, the ratio of syringyl (S) and guaiacyl (G) lignin units was increased. Moreover, the transcript levels of putative silver birch 4CL gene (Bp4CL1) were reduced and contents of cinnamic acid derivatives altered. In the other two Pt4CL1a lines changes were detected in the level of individual phenolic compounds. However, considerable variation was found in the transcript levels of silver birch 4CLs as well as in the concentration of phenolic compounds among the transgenic lines and non-transgenic clones. Wounding induced the expression of Bp4CL1 and Bp4CL2 in leaves in all clones and transgenic lines, whereas the transcript levels of Bp4CL3 and Bp4CL4 remained unchanged. Moreover, minor changes were detected in the concentrations of phenolic compounds caused by wounding. As an overall trend the wounding decreased the flavonoid content in silver birches and increased the content of soluble condensed tannins. The results indicate that by reducing the Bp4CL1 transcript levels lignin composition could be modified. However, the alterations found among the Pt4CL1a lines and the non-transgenic clones were within the natural variation of silver birches, as shown in the present study by the clonal differences in the transcripts levels of 4CL genes, soluble phenolic compounds and condensed tannins.

Highlights

Phenolic compounds form a diverse group of secondary metabolites exhibiting important roles in plant development and environmental adaptation [1,2,3]
The presence of neomycin phosphotransferase II (nptII) was confirmed in the line E5396/4 with Southern blot (S6 Figure in S1 File) and the absence of the Pt4CL1 expression was confirmed with real time RT-PCR (S3 and S4 Tables in S3 File), and the E5396/4 is called nptII line on
The 4-coumarate:CoA ligases (4CLs) isoforms are able to use a variety of hydroxycinnamic acids as substrates, and the extent of gene family expansion and substrate diversity has been found to be connected [8]

Summary

Introduction

Phenolic compounds form a diverse group of secondary metabolites exhibiting important roles in plant development and environmental adaptation [1,2,3]. A benzene ring attached to at least one hydroxyl group is a common characteristic of phenolic compounds, mostly derived from cinnamic acid, generated at the first step of the general phenylpropanoid pathway. Carbon flow through the general phenylpropanoid route is extensive as the hydroxycinnamic acids are utilized in the monolignol biosynthetic pathway, giving rise to the second most abundant organic compound on earth, lignin. The accumulation of lignin in secondary cell walls of vascular plants provides mechanical strength, protection against pathogens and herbivores, and enables the essential transportation of water and solutes. Mechanical wounding can induce production of phenolic compounds which are generally considered to interact in the defence responses. Similar to induced defences caused by herbivory response, the accumulation of phenolic secondary metabolites is species dependent [6, 7]

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